You will definitely find a tripod useful if you're interested in night, close-up or macro photography.

If you're doing a macro shoot you could take 200 or 300 shots before you get something you like (have a look at Luis's November submission in the On-Assignment section to see what I mean) and it is much easier to set up the camera the way you want it and make small adjustments with tripod. It'll also take the weight off your hands.